1. Field of the Invention
The present invention relates to reflectors for use in liquid level gauging systems such as those used in fuel tanks, and more particularly to reflectors that shed bubbles.
2. Description of Related Art
A variety of devices are known in the art for monitoring and detecting liquid levels, for example, for determining the level of remaining fuel in a fuel tank. Of such devices, many include ultrasonic signals to determine liquid levels. Such ultrasonic liquid level gauging systems typically employ ultrasonic reflectors to prevent signal loss at tank full conditions, assisting in calibrating gauges, measuring the speed-of-sound through a fluid, and/or as caps on stillwells.
An ultrasonic liquid level gauging system 1 that is representative of the prior art is shown in FIGS. 2-3. Ultrasonic liquid level gauging system 1 typically includes a transducer 8 that is configured to send and receive ultrasound signals 10 from the bottom of a fluid storage tank or container to the fluid surface. At the fluid surface, the sound typically reflects back to the transducer 8. By monitoring the time it takes for the signal to leave and return to transducer 8, in conjunction with knowing the speed of sound through the fluid, it is possible to calculate the distance from the fluid surface to transducer 8. Such techniques can be used to determine fuel levels in an aircraft fuel tank 3, for example. Typically, transducer 8 is located at or near the bottom of the aircraft fuel tank 3, in order to monitor the fluid level over a range of levels within the fuel tank.
FIG. 3 shows an ultrasonic reflector within the ultrasonic liquid level gauging system 1 of FIG. 2, that is representative of the prior art. Ultrasonic reflectors for this purpose typically include reflector targets 4 located at a predetermined distance D from the ultrasonic transmit and receive transducer 8. Reflector target 4 is typically a flat piece of metal oriented orthogonally to the ultrasonic beam. Reflector target 4 can be oriented within a stillwell 2 as a cap, or independent of a stillwell 2.
As part of the ultrasonic liquid level gauging system 1, FIG. 2 shows a stillwell 2 that is representative of the prior art. Stillwells 2 are hollow tubes disposed in a fluid that can be used in conjunction with flat reflector targets 4. For a system that sends ultrasonic signals 10 from the bottom of a fluid storage, such as an aircraft fuel tank 3, the stillwell 2 is aligned over transducer 8 and extends from the bottom of the storage towards the top of the storage. Stillwell 2 guides the ultrasound signals 10, prevents echoes from tank structures, reduces liquid level slosh above transducer 8, calms liquid surface ripples and reduces bubbles and debris from the path of ultrasound signal 10.
Some stillwells 2 use reflector targets 4 as caps on their top end in order to ensure that a signal is reflected back to the transducer 8 when liquid levels are higher than the top of the stillwell 2. Without such a reflector target 4 cap, ultrasonic signal 10 may not reflect back to transducer 8 once it leaves the stillwell 2 when liquid levels are high, for example when tank 3 is completely full of fuel, signals sent from transducer 8 go directly out of tank 3 without being reflected back, resulting in a signal loss. Such signal loss is undesirable because it can be confused with failure of transducer 8. Unfortunately, typical flat reflector targets 4, used for this purpose, collect bubbles at reflective surface 6 that diminish, distort or eliminate the return ultrasound pulse. In addition, the shape of flat reflective surface 6 limits the reflector target 4 positioning options within a fluid storage container, due to the need for precise alignment.
Reflectors are also used in ultrasonic liquid level gauging systems 1 as velocimeter targets. A submerged velocimeter target, set a known distance from an ultrasonic transmit and receive transducer, can be used to measure the speed of sound in a fluid to improve liquid level monitoring in ultrasonic liquid level gauging system. Velocimeters can be located in a common stillwell with the liquid level gauge or independently. Velocimeters are known in the art to be flat metallic surfaces submerged in fluid. The flat velocimeter targets can experience similar drawbacks as those experienced by the flat reflector caps mentioned above. Typically, flat velocimeter targets pose more drawbacks when located outside of the stillwell because the ultrasonic signals will not be guided by the stillwell. When located outside of the stillwell, the flat target's alignment with the transducer is much more critical.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for ultrasonic liquid level gauging systems that allow for improved performance, including better accuracy and even alignment. There also remains a need in the art for such reflectors that are easy to make and use. The present invention provides a solution for these problems.